Added 14-16

Author: mattpocock

notes/FUTURE.md

@@ -1,19 +1,14 @@
 ## Things to add
 
-- any vs unknown (use casting an error in a catch block as an example)
-- intersection types
 - classes
-- interface extends
 - Omit, Partial, Pick, Required, Record (object-based utility types)
 - ReadonlyArray
-- typeof narrowing
-- instanceof narrowing
-- limits of typeof narrowing (unknown and object)
 
 ## Things NOT to add
 
 These things are out-of-scope, or will be included in other modules
 
+- limits of typeof narrowing (unknown and object)
 - Type predicates
 - Using external libraries and @types
 - discriminated unions

src/10-set.problem.ts

@@ -19,5 +19,5 @@ it("Should give a type error when you try to pass a non-string", () => {
 it("Should be typed as an array of strings", () => {
   const guitaristsAsArray = Array.from(guitarists);
 
-  type cases = [Expect<Equal<typeof guitaristsAsArray, string[]>>];
+  type tests = [Expect<Equal<typeof guitaristsAsArray, string[]>>];
 });

src/10-set.solution.ts

@@ -19,5 +19,5 @@ it("Should give a type error when you try to pass a non-string", () => {
 it("Should be typed as an array of strings", () => {
   const guitaristsAsArray = Array.from(guitarists);
 
-  type cases = [Expect<Equal<typeof guitaristsAsArray, string[]>>];
+  type tests = [Expect<Equal<typeof guitaristsAsArray, string[]>>];
 });

src/14-extends.problem.ts

@@ -0,0 +1,30 @@
+import { Equal, Expect } from "./helpers/type-utils";
+
+/**
+ * Here, the id property is shared between all three
+ * interfaces. Can you find a way to refactor this to
+ * make it more DRY?
+ */
+
+interface User {
+  id: string;
+  firstName: string;
+  lastName: string;
+}
+
+interface Post {
+  id: string;
+  title: string;
+  body: string;
+}
+
+interface Comment {
+  id: string;
+  comment: string;
+}
+
+type tests = [
+  Expect<Equal<User, { id: string; firstName: string; lastName: string }>>,
+  Expect<Equal<Post, { id: string; title: string; body: string }>>,
+  Expect<Equal<Comment, { id: string; comment: string }>>,
+];

src/14-extends.solution.ts

@@ -0,0 +1,31 @@
+import { Equal, Expect } from "./helpers/type-utils";
+
+/**
+ * Here, the id property is shared between all three
+ * interfaces. Can you find a way to refactor this to
+ * make it more DRY?
+ */
+
+interface Base {
+  id: string;
+}
+
+interface User extends Base {
+  firstName: string;
+  lastName: string;
+}
+
+interface Post extends Base {
+  title: string;
+  body: string;
+}
+
+interface Comment extends Base {
+  comment: string;
+}
+
+type tests = [
+  Expect<Equal<User, { id: string; firstName: string; lastName: string }>>,
+  Expect<Equal<Post, { id: string; title: string; body: string }>>,
+  Expect<Equal<Comment, { id: string; comment: string }>>,
+];

src/15-intersection.problem.ts

@@ -0,0 +1,34 @@
+interface User {
+  id: string;
+  firstName: string;
+  lastName: string;
+}
+
+interface Post {
+  id: string;
+  title: string;
+  body: string;
+}
+
+/**
+ * How do we type this return statement so it's both
+ * User AND { posts: Post[] }
+ */
+export const getDefaultUserAndPosts = (): unknown => {
+  return {
+    id: "1",
+    firstName: "Matt",
+    lastName: "Pocock",
+    posts: [
+      {
+        id: "1",
+        title: "How I eat so much cheese",
+        body: "It's pretty edam difficult",
+      },
+    ],
+  };
+};
+
+const userAndPosts = getDefaultUserAndPosts();
+
+console.log(userAndPosts.posts[0]);

src/15-intersection.solution.ts

@@ -0,0 +1,30 @@
+interface User {
+  id: string;
+  firstName: string;
+  lastName: string;
+}
+
+interface Post {
+  id: string;
+  title: string;
+  body: string;
+}
+
+export const getDefaultUserAndPosts = (): User & { posts: Post[] } => {
+  return {
+    id: "1",
+    firstName: "Matt",
+    lastName: "Pocock",
+    posts: [
+      {
+        id: "1",
+        title: "How I eat so much cheese",
+        body: "It's pretty edam difficult",
+      },
+    ],
+  };
+};
+
+const userAndPosts = getDefaultUserAndPosts();
+
+console.log(userAndPosts.posts[0]);

src/16-omit-and-pick.problem.ts

@@ -0,0 +1,16 @@
+import { Equal, Expect } from "./helpers/type-utils";
+
+interface User {
+  id: string;
+  firstName: string;
+  lastName: string;
+}
+
+/**
+ * How do we create a new object type with _only_ the
+ * firstName and lastName properties of User?
+ */
+
+type MyType = unknown;
+
+type tests = [Expect<Equal<MyType, { firstName: string; lastName: string }>>];

src/16-omit-and-pick.solution.1.ts

@@ -0,0 +1,16 @@
+import { Equal, Expect } from "./helpers/type-utils";
+
+interface User {
+  id: string;
+  firstName: string;
+  lastName: string;
+}
+
+/**
+ * How do we create a new object type with _only_ the
+ * firstName and lastName properties of User?
+ */
+
+type MyType = Omit<User, "id">;
+
+type tests = [Expect<Equal<MyType, { firstName: string; lastName: string }>>];

src/16-omit-and-pick.solution.2.ts

@@ -0,0 +1,16 @@
+import { Equal, Expect } from "./helpers/type-utils";
+
+interface User {
+  id: string;
+  firstName: string;
+  lastName: string;
+}
+
+/**
+ * How do we create a new object type with _only_ the
+ * firstName and lastName properties of User?
+ */
+
+type MyType = Pick<User, "firstName" | "lastName">;
+
+type tests = [Expect<Equal<MyType, { firstName: string; lastName: string }>>];